arevolutioner/effective-python-summary

EFFECTIVE-PYTHON-SUMMARY

This book's summary provides insight into the Pythonic way of writing programs: the best way to use Python. It builds on a fundamental understanding of the language that I assume you already have. Novice programmers will learn the best practices of Python’s capabilities.

Brett Slatkin. Effective Python: 90 Specific Ways to Write Better Python, Second Edition (Nazeer Hussain Shaik's Library) (Kindle Locations 229-231).

EFFECTIVE PYTHON SUMMARY

1.PYTHONIC THINKING

1.1. Know the Differences Between bytes and str

To convert Unicode data to binary data, you must call the encode method of str . To convert binary data to Unicode data, you must call the decode method of bytes .

✦ bytes contains sequences of 8-bit values, and str contains sequences of Unicode code points. ✦ Use helper functions to ensure that the inputs you operate on are the type of character sequence that you expect (8-bit values, UTF-8-encoded strings, Unicode code points, etc). ✦ bytes and str instances can’t be used together with operators (like > , == , + , and % ). ✦ If you want to read or write binary data to/from a file, always open the file using a binary mode (like 'rb' or 'wb' ). ✦ If you want to read or write Unicode data to/from a file, be careful about your system’s default text encoding. Explicitly pass the encoding parameter to open if you want to avoid surprises.

1.2. Prefer Interpolated F-Strings Over C-style Format Strings and str.format

f_string = f'{key:<10} = {value:.2f}' c_tuple = '%-10s = %.2f' % (key, value) str_args = '{:<10} = {:.2f}' . format (key, value)

str_kw = '{key:<10} = {value:.2f}' . format (key = key, value = value) c_dict = '%(key)-10s = %(value).2f' % { 'key' : key,'value' : value} assert c_tuple == c_dict == f_string assert str_args == str_kw == f_string

Things to Remember

✦ C-style format strings that use the % operator suffer from a variety of gotchas and verbosity problems. ✦ The str.format method introduces some useful concepts in its formatting specifiers mini language, but it otherwise repeats the mistakes of C-style format strings and should be avoided. ✦ F-strings are a new syntax for formatting values into strings that solves the biggest problems with C-style format strings. ✦ F-strings are succinct yet powerful because they allow for arbitrary Python expressions to be directly embedded within format specifiers.

1.3. Write Helper Functions Instead of Complex Expressions

green_str = my_values.get( 'green' , [ '' ]) if green_str[ 0 ]: green = int (green_str[ 0 ]) else : green = 0

def get_first_int(values, key, default = 0 ): found = values.get(key, [ '' ]) if found[ 0 ]: return int (found[ 0 ]) return default

Things to Remember

✦ Python’s syntax makes it easy to write single-line expressions that are overly complicated and difficult to read. ✦ Move complex expressions into helper functions, especially if you need to use the same logic repeatedly. ✦ An if / else expression provides a more readable alternative to using the Boolean operators or and and in expressions.

1.3. Prefer Multiple Assignment Unpacking Over Indexing

The values in tuples can be accessed through numerical indexes: \

item = ( 'Peanut butter' , 'Jelly' )

first = item[ 0 ]

second = item[ 1 ]

print (first, 'and' , second)

item = ( 'Peanut butter' , 'Jelly' )

first, second = item # Unpacking

print (first, 'and' , second)

Things to Remember

✦ Python has special syntax called unpacking for assigning multiple values in a single statement.

✦ Unpacking is generalized in Python and can be applied to any iterable, including many levels of iterables within iterables.

✦ Reduce visual noise and increase code clarity by using unpacking to avoid explicitly indexing into sequences.

1.4. Prefer enumerate Over range

flavor_list = [ 'vanilla' , 'chocolate' , 'pecan' , 'strawberry' ]

for flavor in flavor_list:

print ( f'{flavor} is delicious' )

for i in range (len(flavor_list)):

flavor = flavor_list[i]

print(f'{i + 1}:{flavor}')

it = enumerate(flavor_list)

print(next(it))

print(next(it))

Things to Remember

✦ enumerate provides concise syntax for looping over an iterator and getting the index of each item from the iterator as you go.

✦ Prefer enumerate instead of looping over a range and indexing into a sequence.

✦ You can supply a second parameter to enumerate to specify the number from which to begin counting (zero is the default).

1.5. Use ZIP to Process Iterators in Parallel

names = ["Cecilia", "Lise", "Marie"]

counts = [len(n) for n in names]

longest_name = None

max_count = 0

for i in range(len(names)):

count = counts[i]

if count > max_count:

longest_name = names[i]

max_count = count

print(longest_name)

#The problem is that this whole loop statement is visually noisy.

To make this code clearer, Python provides the zip built-in function.

zip wraps two or more iterators with a lazy generator.

names = ["Andrey", "Blagovesta", "Boris", "Georgy"]

counts = [len(n) for n in names]

longest_name = None

max_count = 0

for name, count in zip(names, counts):

if count > max_count:

longest_name = name

max_count = count

print(longest_name)